Don't set _POSIX_C_SOURCE for VXI/RPC related files.

Make vxi.h the first #include in all affected files and #undef the
_POSIX_C_SOURCE macro in vxi.h.

This avoids various build issues on e.g. FreeBSD or Mac OS X where
setting _POSIX_C_SOURCE leads to the unavailability of certain types
such as u_long (as used in the VXI/RPC code).

src/scpi/scpi_vxi.c

@@ -20,9 +20,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "vxi.h"
 #include <rpc/rpc.h>
 #include <string.h>
-#include "vxi.h"
 #include <libsigrok/libsigrok.h>
 #include "libsigrok-internal.h"
 #include "scpi.h"

src/scpi/vxi.h

@@ -3,6 +3,8 @@
  * It was generated using rpcgen.
  */
 
+#undef _POSIX_C_SOURCE
+
 #ifndef _VXI_H_RPCGEN
 #define _VXI_H_RPCGEN
 

src/scpi/vxi_clnt.c

@@ -3,8 +3,8 @@
  * It was generated using rpcgen.
  */
 
-#include <memory.h> /* for memset */
 #include "vxi.h"
+#include <memory.h> /* for memset */
 
 /* Default timeout can be changed using clnt_control() */
 static struct timeval TIMEOUT = { 25, 0 };